Delay circuit for receiver-indicator



Sept. 2, 1958 F. DAVIDOFF DELAYl CIRCUIT FOR RECEIVER-INDICATOR SePL 2\,1958 n F. DkvlDoFF DELAY CIRCUIT FoR RECEIVER-INDICATOR 2 Sheets-Sheet 2Filed Oct. 4, 1954 www INVEN'roR DELAY CrRcUrr non RECEIVER-INDICATORFrank Davidof, Clifton, N. J., assignor to International Telephone andTelegraph Corporation, New York, N. Y., a corporation of MarylandApplication Qctober 4, 1954, Serial No. 460,149

Claims. (Cl. 250-27) This invention relates to a delay circuit for areceiverindicator and particularly to a continuously variable delaycircuit.

More particularly, this invention relates to a continuously variabledelay system which is controlled by a single shaft. j l

It is often necessary in modern communication equipment to providecontinuous delay circuits for measuring time differences with a highdegree of precision. This invention finds its utility in such systems.An example of such a system is the hyperbolic navigation system known asloran in which it is necessary to measure the time difference betweentwo received pulses. Measurement of time is as large as 15,000microseconds (psec.) with a maximum desired accuracy of at least .5,usec. In loran, two transmitting stations are oriented to transmitpulses at given time intervals, which pulses are received by a vesselsuch as an airplane, and, at the receiver the time difference betweenthe two received pulses is analyzed from which a line of position of thecraft is determined with respect to the two transmitting stations. Thetransmitting stations are referred to as master and slave stationsrespectively. The master station transmits a pulse of repetitionfrequency of about 25 pulses per second (P. P. 8.). The slave stationreceives the pulse delayed by the time of propagation from one stationto the other, waits one half the pulse repetition interval plus a givenperiod of time called a coding delay, and then transmits its pulse. Thereceiving equipment located in the vessel synchronizes its timingcircuits with the master pulse and accurately measures the delay betweenthe master and slave received pulses. A detailed explanation o-f theloran system may be found in the book entitled Loran, RadiationLaboratory Series 4, rst edition.

The delay circuit, which is used to measure the delay between thereceived pulses, should be controlled by a single shaft to permitadaptation to an automatic tracking device. The conventional circuit foraccomplishing this type of control is a variable phase shifting circuit.It is known that phase Shifters can provide a given amount of delay foreach revolution and any desired delay can be obtained by rotating thephase Shifters the required number of revolutions. The output of suchphase shifter is a delayed sine wave and the duration of each cyclerepresents the delay of one revolution. Generally, a marker signal isgenerated by each cycle, having the same delay as the cycle. The problemin using this output is that of selecting the desired marker signal fromthe chain of delayed marker signals over the entire delay range. Thisproblem has been solved by gearing other phase Shifters, operating atdifferent frequencies, to the iinal phase shifter so that the output ofthe first phase shifter 'selects the output of the second one; theoutput of the second selector selects the output of the third, and soforth until the nal phase shifter output has been selected. This type ofdelay device is encumbered with complex and costly gearing mechanisms.Furthermore,

States Patent Patented Sept. 2, 1958 rlice used in conjunction withloran, may be characterized as a double-scale time modulation circuit.The double scale circuit utilizes a iine control circuit which producesa chain of delayed marker pulses and a coarse control circuit, which,broadly, selects a desired one of the marker pulses. In such doublescale circuits, considerable diiiiculty has been encountered incoordinating the Acontrols to achieve continuous delay over the entirerange. For example, when the tine control is increased to a timeintervai exceeding that between two fixed pulses, the coarse controlmust be advanced to select the next pulse. This requires that thesetting on the tine scale be simultaneously reduced from maximum to zeroin order that approximately continuous movement of the time delay beachieved. Although mechanical devices employing cams, switches, andpotentiometer-s covering 3591/2 have been constructed to accomplishthis, such apparatus has not proved satisfactory.

Accordingly, it is an object of this invention to provide a delay devicewhich is less expensive and much simpler than known continuouslyvariable delay devices.

It is a further object of this invention to provide a delay circuit ofthe wave form generator type which eliminates the need for suchprecision equipment as mentioned above and which completely overcomesthe above-mentioned diiiiculty.

in accordance with an aspect of this invention, there is provided acontinuous delay circuit comprising a pair of normally inoperativevariable time delay circuits. The delay circuits are rendered operativeby applying to them, rst and second trains of pulses of similarperiodicity, but one train of pulses being time displaced from the otherby a given amount. The maximum delay of the delay circuits is less thanthe repetition frequency of the pulses but greater than the timedisplacement between the pulse trains. The delays are controlled so thatthe delay of one circuit is equal to the period of time displacement atthe time the other delay is initiated. The delays of both circiuts areterminated simultaneously in a region of overlap of the delays, wherebya continuous delay is achieved by successively switching from thecircuit having the longer delay, to the circuit having the shorterdelay.

The above-mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will be best understood by reference to the following descriptionof an embodiment of the invention taken in conjunction with theaccompanying drawings, in which:

Fig. l is a schematic diagram of the continuousdelay circuit forming oneembodiment of the invention; and

Fig. 2 is a timing diagram showing the wave forms appearing at thedesignated places in Fig. l.

Referring now to Fig. 1, there is shown a continuous delay circuit foruse in conjunction with a loran receiver indicator. However, as mentinedabove, the invention is not restricted to the loran receiver-indicatorbut will be described in connection therewith to facilitate anunderstanding of the invention. The delay circuit comprises a frequencydivider 1 which may comprise two sections, for producing respectiveoutputs at different pulse repetition frequencies. The frequenciesrecited in the following description are only by way of example andother frequencies may be used with equal facility. A frequency common tothe lorain system is 100 kilocycles (kc.) and therefore Fig. 1 shows aninput to the frequency divider of 100 kc. If desired, separate pulseproducing circuits may be utilized in place of the frequency divider.The frequency divider 1 produces at one output thereof, pulses having arepetition frequency of 5000 per second (5000 P. P. S.) and spaced 200psec. apart for triggering Hip-flop circuit 2. The flip-flop circuit 2is a conventional circuit and, by way of example, may be anEccles-Jordan multivibrator. The flip-flop circuit 2 produces two chainsof marker pulses, the pulses of each chain being spaced apart by 400lusec. (using the above example), but time displaced from the otherchain by 200 psec. as shown at lines A and B of Fig. 2. The outputs fromthe flip-flop circuit are differentiated to produce sharp pulses asindicated by the lines A and B. The differentiating circuits are notshown separately and may be considered as part of the flip-flop circuitillustrated by the block diagram. The differentiated outputs from theflip-flop circuit are applied as triggering pulses to circuits 3 and 4,respectively. The circuits 3 and 4 are monostable variable-widthwaveform generators. By varying the width of the output pulses of suchgenerators, the delay of the trailing edge with respect to the leadingedge of each of such pulses is controlled. By differentiating the outputpulse, a delayed pulse corresponding in time to the trailing edge of theoutput pulse is thus obtained. A very satisfactory variable widthgenerator is the phantastron which is a simple electronic circuitcapable of producing a variable time delay, stable over relatively longperiods. The operation of the phantastron is well known and adescription thereof may be found in Electronics Magazine, April 1948, atpages 100-107. The most satisfactory phantastron circuit, for thisinvention, uses a pentode, and the output pulse width is controlled by avoltage applied to the plate circuit of the pentode. Therefore, theextent of time delay may be variably controlled by a potentiometerconnected in the .plate circuit of the pentode.

Thus, the output pulses from the flip-flop circuit 2 (shown at lines Aand B) are applied to two identical phantastrons circuits 3 and 4, whichare thereby alternately triggered. The delay range of the phantastronsis extremely linear except in the region of `minimum delay. For a delayrange of 200 ptsec. the phantastron is best operated, from thestandpoint of linearity, from a minimum of l lusec. to a maximum of 220psec. delay. The phantastrons 3 and 4 have been designated in Fig. 1 asthe fine delay circuits, consistent with the language of the art, toindicate the marker pulse producing circuits. lf the delay range of eachphantastron circuit 3 and 4 is adjusted to lusec. minimum and 220 lusec.maximum, and assuming triggering pulses spaced 400 psec. apart are used,as suggested in the example, there will be an interval of 10 nsec.during which both delay circuits are producing a pulse. The constants ofthe two phanastrons are so chosen, with respect to the delay controlpotentiometers, that they will return to their inoperative statesimultaneously when triggered into operation by pulses spaced in time bythe chosen interval. During the interval of overlap the trailing edgesof both pulses appear at the same absolute time and either circuit maybe used to provide the output pulse. By way of example, the timingdiagram of Fig. 2 shows at line C, phantastron 3, at a delay of psec.and at line D, phantastron 4 at a delay of 215 psec. Since the triggerpulse shown on line B is first in time, it will trigger phantastron 4,and phantastron 4 will produce on output, until a change is caused bythe timing parameters of the circuit, and 200 psec. after phantastron 4has been triggered, opera- CTL tion of phantastron 3 will be initiatedby the pulse shown on line A. The maximum delay (220 nsec.) of eachphantastron circuit (indicated by the trailing edge of the output pulse)is selected to be less than the period of the marker pulses (spacedapart 400 psec.) but greater than the displacement between the twotrains of pulses (200 used). The pulses are differentiated bydifferentiating circuits 5 and 6 respectively, and the resultant pulseswhich correspond to the trailing edges of the output waveform from thephantastrons are indicative of the time delay. The timing diagram (Fig.2) illustrates the differentiated pulses at lines E and F.

The delays produced by the phantastrons 3 and 4 are controlled bypotentiometers 7 and 8, respectively. The two potentiometers 7 and 8 arecontrolled by a single shaft S and are preferably arranged so that thetermination of one potentiometer winding is opposite the termination ofthe other winding. Obviously, instead of two potentiometers, one couldbe satisfactorily employed having a double wiper. The delays produced bythe phantastrons are directly proportional to the potentiometervoltages, and the arrangement of the potentiometers is such that while amaximum Voltage is being applied to one phantastron, a suitable minimumvoltage, to produce a minimum delay, is being applied to the other. Eachof the potentiometers, as shown, has one terminal connected to groundand the other terminal connected to a positive source of voltage supplyindicated by the symbol on the drawing. It has been found that asuitable minimum voltage is developed by the potentiometer when theWiper arm thereof has travelled approximately 20 away from the groundterminal. Thus, one wiper arm would be at the maximum voltage position,or at the position which causes its associated phantastron to producemaximum delay, while the other .wiper arm is at a suitable voltageposition to cause its associated phantastron to produce a minimum delay.

To review one complete cycle of operation by further pursuing theexample, assume that phantastron 3 is initially adjusted by thepotentiometer 7 to produce a 15 usec. delay. Accordingly, potentiometer8 is adjusted to produce a 215 psec. delay. As the shaft S is rotated,.thus varying the voltages produced by the respective potentiometers,the delays of the phantastrons are correspondingly varied since thedelays thereof are proportional to'the potentiometer voltages. Referringto the Figs. 1 and 2, it is observed that the wiper arms of thepotentiometers are moving in the duration of more positive voltage, asindicated by the arrow, upon rotation of the shaft. If the wiper arm ofpotentiometer 7 must traverse 20 ofthe resistor winding before thevoltage developed by the potentiometer 7 is suicient to causephantastron 3 to produce a useful delay, then prior to attaining thisposition, phantastron 3 is producing no useful delay, While the delayproduced by phantastron 4 is increasing. By further rotating the shaftso that the wiper arm of potentiometer 7 has travelled past 20 of theWinding, a sufficient voltage will be applied to phantastron 3 to causeit to produce a useful delay, for example, 15 psec. as shown at line Cof Fig. 2. At that time, the wiper arm of potentiometer 8 will beapplying almost a maximum voltage to phantastron 4 causing it to producea delay of 215 psec. Further rotation of the shaft will causephantastron 4 to continuously increase its delay to its maximum, whichis assumed at 220 psec., while causing phantastron 3 to increase from 15psec. to 20 lusec. Continued rotation of the shaft will cause thephantastron 3 to go through a complete cycle of delay and returning tothe original condition. During this time phantastron 4 will beinoperative to produce effective delay until phantastron 3 reaches about215 psec. delay, at which time the switch will be returned to contact13. Thus, it is observed that both phantastrons are producing delayssimultaneously over a given period and that the trailing edges of thetwo pulses are coincident. It is over thisy givenk periodthatlswitclr-over from one delay circuit to the other is effected,Awhereby either trailing edge is selected and correspondsv to the timedelay.

During the period while the-delayed pulse fromA phantastron 3 isutilized, cam-operated microswitchr 9- is in the position indicated,making contact with the output lead from differentiating circuitl 5.vThe microswitch 9 is operated by a cam 11, mechanically coupled to thecontrol shaft S, which actuatesY a`V cam follower 12 to operate themicroswitch. 9. The cam' is designed to operate switch. 9, to produceswitch-over, at the time when both phantastrons are producing delays;and switchover is from. the phantastron producing, maximum delay to thephantastron producing minimumdelay. In the describedY exampleswitch-over isv eifected preferably at the time phantastron. 3 isproducing 15 ,usec delay andbefore phantastron 4 has reached its maximumdelay of 220l ,usec. The delayed output. from phantastron 3 is thenutilized until it approaches maximum at which time switch-over tocontact 13 will be initiated by the cam 11, and the output fromphantastron 4, which is then near to its minimum delay, will beutilized. Thus, the two phantastron circuits provide a single,continuous repetitive delay with the only requirement being that thetransition take place during the interval when both phantastron circuitsare producing a delay and having time-coincident trailing edges.

The circuit controlled by the cam-operated microswitch 9 to selecteither one of the delay circuits may be very simple. For example, ifeach delay circuit output is fed to the grid of a tube and the plates ofthe tubes are tied together, the microswitch may be used to bias one orthe other of the tubes and allow only one signal to be transmitted.

The resultant output of the delay circuits is a chain of marker pulsesspaced 400 ,usec. apart from each other as shown at G of Fig. 2. Theentire chain can be advanced or retarded in time by rotating the controlshaft S, and a xed delay of all the pulses of the chain is obtained whenthe shaft is in any one given position.

While the delay of the pulse trains operating the two tine delaycircuits may be of any chosen value, the choice of a delay equal tosubstantially one half the pulse repetition period is advantageous, asthen the interval of overlap operation of the two delay circuits may bekept small.

The continuous delay system is advantageously used in the loran systemby selecting a desired one of the delayed markers to measure thedistance between two received pulses. The desired marker is selected bymeans of another phantastron 14 which=corresponds to the coarse control.The phantastrons 3 and 4 correspond to the line control of the two scalemarker system; i. e. phantastrons 3 and 4 produce the marker pulses andphantastron 14 corresponds to the coarse control which is the secondscale of the two scale system; i. e., phantastron 14 is instrumental inselecting a desired one of the marker pulses. Phantastron 14 iscontrolled by a l0 turn helical potentiometer 15, which is also gearedto the shaft S but with a different gear ratio. The output ofphantastron 14 is adjusted by the control voltage applied thereto frompotentiometer 15 to track along with the 400 lusec. marker pulses. For adelay range of 16,000 lasec., the gear ratio for potentiometer 15 wouldbe 4:1 so that its wiper will traverse 1A the distance traversed by thewipers of potentiometers 7 and 8. Phantastron 14 operates similarly tophantastrons 3 `and 4 in that the extent of time delay is controlled bypotentiometer 15 and it is triggered into operation by a pulse. Thispulse occurs once per loran cycle at the start of the slave half cycle,as shown at line H.

As mentioned above, the nominal loran repetition rate is P. P. S., or 1pulse per 40,000 lusec. The phantastron 14 always selects the samemarker pulse as the entire delay range is traversed because of thecommon control coupledV tothe several potentiometers and cam. It isdescribed` above thatJ the' marker pulses, as shown at line G,'rnay beadvancedY or retarded by rotation of the shaft S. Since the'potentiometer 1S is coupled to the shaft the delay producedby'phantastron 14 is correspondingly advanced or retarded the sameamount. Thus, if it isl desir-edv to select the marker pulse P, shown atline G,.the delay of phantastron 14 is adjusted so that the marker pulseappearing after its trailing edge will 'be selected. If the shaft isrotated to advance the delay, it is seen that both the trailing edge ofthe output pulse from phantastron 14 and the marker pulse are advanced.Similarly, if they shaftl is rotated in the opposite direction, both thepulse P and the trailing edge of the output from phantastron 14 are'retarded; therefore, the marker pulse P is always'. selected duringtraversal of the delay range.

The selected pulse. P may be. passed to van indicating circuit by anysuitable circuit well known. to the art. For example, the? selectorcircuit may be an Eccles-Tordan bistable multivibrator shown as a markerselector circuit 16. With this type of circuit, the output from thecoarse phantastron 14 would be differentiated and the pulsecorresponding to the trailing edge would be employed to trigger one sideof the multivibrator. The selected marker pulse would then trigger themultivibrator to its other stable condition. The output from themultivibrator would then be a pulse having one edge corresponding to themarker pulse as shown at line I. The differentiated output is utilizedin the utilization circuit.

While I have described above the principles of my invention inconnection with specic apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationto the scope of my invention as set forth in the objects thereof and inthe accompanying claims.

What is claimed is:

l. A device for producing output pulses having a continuously adjustabledelay over a predetermined time interval, comprising a pulse source forproducing iirst and second trains of pulses each with a predeterminedrepitition rate, said pulse trains having a predetermined timedisplacement with respect to one another, rst and second normallyinoperative, variable delay circuits each adjustable from a minimum to amiximum delay and constructed to terminate simultaneously when renderedoperative at times equal to said predetermined time displacement themaximum delay of each delay circuit being greater than saidpredetermined time displacement and less than said predeterminedrepetition rate, means for simultaneously adjusting the delays of bothsaid delay circuits so that one circuit is near its maximum delay 'whenthe other circuit is at its minimum delay, means for applying said pulsetrains to said first and second delay circuits, respectively, to renderthem successively operative, whereby output pulses having the same timeposition are produced during a period of overlap of operation of saiddelay circuit, an output circuit selectively connected to the outputs ofsaid delay circuits, and means for switching the connections of saidoutput circuit from the delay circuit having the longer delay to thedelay -circuit having the shorter delay during the overlap interval.

2. A device according to claim l, wherein said delay circuits arevoltage controlled their delays being proportional to the magnitude ofand applied voltages, said means for adjusting said delays comprising asource of variable voltage coupled to each of said delay circuits, andmeans for continuously adjusting the voltages from said sourcesinversely with respect to one another.

3. The delay circuit according to claim 2, wherein said source ofvariable voltage comprises a pair of potentiometers coupled respectivelyto said pair of delay circuits, and said adjusting means comprising asingle shaft 17 coupled to both said potentiometers, the wiper contactsof said potentiometers being adjusted so that upon rotation of saidshaft the varying voltages applied to the respective delay circuitscause one delay circuit to vary from minimum to maximum, and cause theother delay circuit to vary from maximum to minimum.

4. The circuit according to claim 3, wherein said delay circuitscomprise phantastrons capable of producing variable width pulses, thewidth being proportional to the magnitude of control voltage appliedthereto, and corresponding to the time delay, said potentiometers beingadjusted so that the trailing edges of said pulses are coincident intime whereby said trailing edge serves as a time delay marker.

5. The circuit according to claim 4, and further comprising meanscoupled to the outputs of said phantastrons for differentiating thewaveforms produced thereby and obtaining a pulse corresponding to thetrailing edge of said waveform, a cam coupled to said shaft, a utilitycircuit, switching means controlled by said cam and coupled T8 betweenthe output of said differentiating means and the input of said utilitycircuit, said cam being adjusted to actuate said switch so that the delay circuit varying from minimum to maximum is successivelyV coupled tosaid utility circuit.

Referenees Cited in the me of this parent UNITED STATES PATENTS2,466,044. Schoenfeld Apr. 5, 1949 2,534,872 Meacham Dec. 19, 19502,560,600 Schafer July 17, 1951 2,614,218 Hancock Oct. 14, 19522,660,672 Urtel Nov. 24, 1953 2,665,410 Burbeck Jan. 5, 1954 2,685,027Alvarez July 27, 1954 2,697,797 Holmes Dec. 21, 1954 2,710,914 OkrentJune 14, 1955 2,716,236 Reinish et al Aug. 23, 1955

